Deconfigure thread mode when the loop thread ends.

Threaded mode is deconfigured when the mosquitto_loop_start() thread ends,
which allows mosquitto_loop_start() to be called again.

Closes #2242. Thanks to Timo Lange.

ChangeLog.txt

@@ -37,6 +37,8 @@ Client library:
   connect successfully without verifying certificates, because they were not
   configured.
 - Disable TLS v1.3 when using TLS-PSK, because it isn't correctly configured.
+- Threaded mode is deconfigured when the mosquitto_loop_start() thread ends,
+  which allows mosquitto_loop_start() to be called again. Closes #2242.
 
 Clients:
 - mosquitto_sub and mosquitto_rr now open stdout in binary mode on Windows

lib/thread_mosq.c

@@ -129,6 +129,9 @@ void *mosquitto__thread_main(void *obj)
 		/* Sleep for our keepalive value. publish() etc. will wake us up. */
 		mosquitto_loop_forever(mosq, mosq->keepalive*1000, 1);
 	}
+	if(mosq->threaded == mosq_ts_self){
+		mosq->threaded = mosq_ts_none;
+	}
 
 	return obj;
 }